The principle of illuminating an object to acquire images dates back over one hundred years. Imaging is a general term used for a variety of techniques, technologies and fields associated with the acquisition of two dimensional and three dimensional representations of an object or subject. Many imaging techniques used to acquire analog or digital representations of the surface of an object require illumination. Most imaging techniques used to acquire analog or digital representations of planes of structures inside an object require illumination by a beam capable of penetrating the object and being either transmitted or reflected from the object. For example, in X ray transmission imaging a beam of X rays is transmitted through an object and an image is generated based on X ray attenuation data.
Medical imaging refers to the techniques and processes used to create images of the human body (or parts thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology).
One example of a medical imaging technology is Computed Tomography (“CT”). The basic principle behind CT scanning includes characterizing each of a set of volume elements in a volume being scanned by transmitting radiation through each of the volume elements from multiple angles. Each exposure at each angle of a CT scan produces a one or two dimensional image on a sensor, where the intensity of exposure on a sensor element of the sensor array indicates an average attenuation of a ray of transmitted caused by matter within the scanned volume along a direct path between the radiation source and the sensor element. Estimation of density or other attenuation characteristics of individual volume elements may be achieved using a back projection process on a set of collected attenuation data. A variety of image filtering and 3D rendering techniques may be used to convert the collected attenuation data into a 3D representation of the internal structures of a scanned object.
Early generation CT scanners had a one dimensional detector array and were capable of scanning one axial slice of the subject at a time. More recent CT scanners have a two dimensional detector array comprising multiple rows of detector elements. These scanners, usually referred to as multislice or multidetector CT scanners, are capable of scanning multiple substantially parallel slices of the subject simultaneously. Further, CT scanners with a large number of detector rows are typically referred to as cone beam scanners. Cone beam scanners image a whole volume at a time.
Some CT scanners use a “step and shoot” protocol. In this protocol the gantry rotates about a stationary subject to generate a single or multiple images of the scanned subject, the subject is translated relative to the gantry, the gantry rotates again to generate images of an adjacent region, etc. Other CT scanners use a helical or spiral mode wherein the subject is being translated relative to the gantry while the gantry rotates and attenuation data is acquired.
Turning now to the attached figures:
FIG. 1 shows the geometry of a prior art single source cone beam CT scanner 9. X ray source 10 emits a beam of X radiation 12 in the direction of detector array 14. Typically the source-detector pair is mounted on a rotating gantry and a subject to be examined 18 is positioned between the source and the detector. Detector array 14 may be composed of an array of discrete elements arranged in rows and columns, a flat panel detector or the like. The array may have a spherical or arc shape centered about the focal spot (as shown), be planar or have other surface curvature. Herein below we refer to “rows” of the detector as the X direction of the detector perpendicular to the rotation axis (Z direction).
In many single source CT scanners, an X ray source and arc shaped array detector are both mounted on a gantry and made to rotate about a subject to be scanned. The beam is shaped by a collimator 16 positioned between the X ray source and the subject. The collimator is designed so as to confine X ray beam projection onto the detector area (or smaller area), thereby limiting radiation going through the subject to only radiation useable for image reconstruction. Collimators typically include blades movable in a direction parallel to the rotation axis (Z axis) to increase or reduce the volume scanned in one rotation as needed.
CT scanners using multiple cone beam sources are also known in the art. Beam geometry of a CT scanner arrangement that employs multiple sources distributed along an axis parallel to the rotation axis (Z axis), such that the multiple sources irradiate a common detector array, is shown in FIGS. 4a and 4b and disclosed in application US 2006/285633 A1 to Sukovic et. al., WO 2006/038145 A to Koken at. al. and WO 2008/122971 to Dafni et. al—incorporated herein by reference. However, CT scanners of such design are not yet available commercially and are not known to have yet been actually built. One of the complexities associated with CT scanners including multiple beam sources is proper collimation.
Today, adjustable synchronized collimation of multiple beams is problematic and requires multiple highly matched collimators driven by either the same or highly synchronized control signals. There is a need in the fields of illumination and imaging for methods, apparatus and systems for providing adjustable collimation of beams produced by multiple beam sources.